I am a submissive and I am also somewhat new to the role. I have been in relationships, where I have been the sub, but not like said out loud. She has to want the role. It is not something that can just be jumped into lightly. She has to be commited to it. It is something you are, not something to play around with. She needs to know her place! Good Luck!
Why not get someone who's going to be a submissive instead of training someone to be? Might save a lot of hassle.